Modulation of electrically induced permeabilization and fusion of Chinese hamster ovary cells by osmotic pressure

Cells can be transiently permeabilized by application of high electric pulses of short duration. A direct consequence of this treatment is to induce a fusogenic state in the pulsed membrane. The molecular events underlying these phenomena remain to be explained. During our work, we investigated the effects of pulsing buffer osmotic pressure on both electric field induced permeabilization and fusion of Chinese hamster ovary cells growing either in monolayers or in suspension. Osmotic pressure has no effect on the induction step of permeabilization, but its increase was shown to inhibit the expansion step and to decrease the efficiency of the resealing phase. Fusion efficiency was greatly affected by the osmotic pressure and by the physiological state of the cells. When cells were grown plated and when intercellular contacts were spontaneous and present during pulsation, increasing the osmotic pressure resulted in an increase in the fusion index. The opposite effect was observed for cells growing in suspension and brought into contact after pulsation. These results were tentatively explained in terms of the effect of the osmotic pressure on the membrane organization and cell-cell contact quality.